Method of reserving network bandwidth resources, and communications system and network device using the same

ABSTRACT

A communications system whose bandwidth resources can be used more efficiently by reserving them on an individual path basis. Upon receipt of a bandwidth reservation message, a path setup initiator examines the message and thereby recognizes that the local station device is the egress node of a specified logical network segment. It then consults a topology database to retrieve hop counts of the source station device, which reveals, for example, that a first ringlet has a smaller hop count than a second ringlet. The path setup initiator sends a working path setup message to the ingress network device over the first ringlet, as well as a protection path setup message to the same ingress device over the second ringlet. Upon receipt of those messages, a bandwidth reservation unit reserves a working path bandwidth on the second ringlet, as well as a protection path bandwidth on the first ringlet.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefits of priority fromthe prior Japanese Patent Application No. 2005-285984, filed on Sep. 30,2005, the entire contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a communications system, a networkdevice, and a method of reserving bandwidth resources. Moreparticularly, the present invention relates to a Resilient Packet Ringcommunication system that transports packets over a redundant ringnetwork. The present invention also relates to a network device, as wellas to a method of reserving bandwidth resources, for use in an RPRsystem.

2. Description of the Related Art

Ring network systems based on the Synchronous Optical Network (SONET) orSynchronous Digital Hierarchy (SDH) standards have been the mainstreamarchitecture of long-haul backbones for wide-area network service.Another technology called “Resilient Packet Ring” (RPR) is gaininginterest in these years as an alternative to SONET/SDH systems. RPR is anew data transmission technique currently in the process ofstandardization by an IEEE committee. The IEEE 802.17 RPR standardoffers protocols of Media Access Control (MAC) sub-layer, part of layer2, like the Ethernet (registered trademark of Xerox Corporation) in LANenvironments. RPR technology takes advantage of a ring topology,combined with an existing technique for layer 1.

RPR assumes the use in a metropolitan area network (MAN). It is possibleto construct an RPR network on an existing backbone with a hierarchy oftransmission rates, such as Optical Carrier (OC-n) of SONET networks orSynchronous Transport Module (STM-n) of SDH networks. 10-GigabitEthernet (10 GbE) may also be used as another option for layer 1(physical layer) architecture. Such existing ring networks carryIEEE802.17 MAC frames (or RPR frames), thereby realizing “RPR overSONET/SDH,” “RPR over GbE,” or the like.

FIG. 10 provides an overview of an RPR network. This RPR network 100includes four stations S1 to S4 and fiber optic links interconnectingthose stations in a dual ring topology. Part of data traffic travelingover the ring network is dropped (i.e., split off) to tributaries atthose stations S1 to S4. The stations S1 to S4 also allow incoming datatraffic from tributaries to be added to the main data traffic on thering.

The dual RPR ring consists of two unidirectional ringlets, Ringlet0 andRinglet1, to transport packets in opposite directions. In the example ofFIG. 10, Ringlet0 runs counterclockwise while Ringlet1 runs clockwise.Ringlet0 and Ringlet1 serve as a working system and a protection system,respectively. RPR networks transport and deliver data in “packets,”whereas SONET/SDH networks do the same in “streams” each accommodating aplurality of OC or STM channels.

The RPR architecture permits packets to have different classes forbandwidth control purposes. FIG. 11 enumerates RPR classes of service.Specifically, there are three class definitions: Class A, Class B, andClass C. Class A offers bandwidth-guaranteed service using previouslyreserved bandwidth resources for packet transport. This class of serviceminimizes end-to-end delays and jitters.

More specifically, Class A is divided into two subclasses A0 and A1. Ofall classes, Class A0 packets enjoy the highest priority. Bandwidthreserved for Class A0 is for exclusive use by Class A0 services; thatis, two or more Class A0 paths can use the same reserved bandwidth, butother classes of service cannot.

Class B is also divided into two subclasses: Class B-CIR (CommittedInformation Rate) and Class B-EIR (Excess Information Rate). Both ClassA1 and Class B-CIR provide bandwidth-guaranteed services, but theirreserved bandwidth resources may be used by other classes (i.e., theyare for non-exclusive use). Class B-EIR and Class C (Class C-EIR), onthe other hand, do not guarantee the bandwidth that they claim to offer.Instead, those classes offer best-effort transport service usingremaining bandwidth.

The system operator provisions, if necessary, a new Class A0 bandwidthfor a station, taking into consideration every existing Class A0 path oneach ring. The operator performs this task by using his/her terminalconsole to send bandwidth configuration commands to that station. Thereceiving station then notifies every peer station of the provisionedbandwidth, so that the Class A0 bandwidth for that station will bereserved throughout the ring network.

FIG. 12 shows a conventional way of reserving bandwidth. The illustratedRPR network 110 is formed from six stations S1 to S6 interconnected byfiber optic links in a dual ring topology. The two ringlets, namedRinglet0 and Ringlet1, transport packets in the counterclockwise andclockwise directions, respectively.

Suppose now that a new path P1 has to be added to transport Class A0packets from station S3 to station S4 at 100 Mbps. The system operatorenters commands to his/her terminal console 103 to configure the ingressstation S3, so as to provision a 100-Mbps bandwidth resource for the newpath P1. The provisioning of this 100-Mbps bandwidth is reported to allother stations, thus reserving 100 Mbps for Class A0 service on bothRinglet0 and Ringlet1.

For an example of such an existing RPR-based technique, see JapanesePatent Application Publication No. 2003-249940, paragraph numbers 0008to 0010, FIG. 1. This publication discloses a technique for realizingdynamic multicast routing control with a reduced signal processingworkload.

One problem of the above-described conventional techniques for RPRbandwidth reservation is their inefficient use of bandwidth resources.Specifically, the existing techniques reserve extra bandwidth on bothRinglet0 and Ringlet1 when adding a new path P for Class A0 traffic.FIG. 13 shows this problem with conventional bandwidth reservation. Inthe illustrated RPR network 110, two hosts H3 and H4 are connected tostations S3 and S4, respectively. These hosts H3 and H4 belong to afirst virtual LAN (VLAN) domain, VLAN1. VLAN is a logical networksegment in which stations can communicate with each other as if theywere in a physically closed network. There is another host H2 connectedto station S2. The hosts H2 and H3 belong to a second virtual LANdomain, VLAN2, meaning that they can communicate with each other as ifthey were in another closed network.

VLAN1 uses a path P1 from station S3 to station S4, while VLAN2 usesanother path P2 from station S2 to station S3. Suppose now that thefirst path P1 needs 100 Mbps for its Class A0 traffic, and that thesecond path P2 needs 50 Mbps for its Class A0 traffic. Suppose also thatthe ringlets have a capacity of 100 Mbps for each.

Both VLAN1 path P1 and VLAN2 path P2 are used as working paths. Since P1does not overlap with P2, the above bandwidth requirements are supposedto be satisfied theoretically. That is, the network must be able totransport packets from S3 to S4 at 100 Mbps concurrently with anotherpacket traffic from S2 to S3 at 50 Mbps.

The conventional bandwidth reservation techniques, however, allocates100-Mbps bandwidth, not only to the first path P1 between S3 and S4, butalso to the other links on Ringlet0 and Ringlet1, including the secondpath P2 between S2 and S3. The second path P2 with a capacity of 50 Mbpscannot be established because the bandwidth resource of the link betweenS2 and S3 has already been exhausted.

As can be seen from the above discussion, the conventional networksystem allocates its bandwidth on an entire ring basis, rather thanreserving path bandwidth on an individual link basis. Such inefficientuse of bandwidth spoils operability of the ring network.

SUMMARY OF THE INVENTION

In view of the foregoing, it is an object of the present invention toprovide an RPR communications system whose bandwidth resources can beused more efficiently by reserving them on an individual path basis.

It is another object of the present invention to provide an RPR networkdevice which enables more efficient use of available bandwidth resourcesby reserving them on an individual path basis.

It is yet another object of the present invention to provide a bandwidthreservation method for an RPR network which enables more efficient useof available bandwidth resources by reserving them on an individual pathbasis.

To accomplish the first object stated above, the present inventionprovides a communications system transporting data over a redundant ringnetwork. The ring network is formed from first and second ringletsrunning in opposite directions. The communications system has aplurality of station devices and a plurality of transmission mediainterconnecting the station devices to form the first and secondringlets.

Each station device has a bandwidth reservation initiator that sends outa bandwidth reservation message in both ring directions. This bandwidthreservation message contains a source identifier, a logical networkidentifier, and a bandwidth reservation value to announce how muchbandwidth should be reserved for a network path. Also contained in eachstation device is a topology database that manages hop counts of otherstation devices on the ring network. The hop counts include first hopcounts measured along the first ringlet and second hop counts measuredalong the second ringlet. A path setup initiator, another elements ofthe station devices, examines a source identifier and logical networkidentifier in a bandwidth reservation message received from otherstation devices, thereby recognizes that the local station device is anegress node of a logical network segment specified in the receivedbandwidth reservation message. It then consults the topology database toretrieve the first and second hop counts of the source station device ofthe received bandwidth reservation message. If the retrieved first hopcount is smaller than the retrieved second hop count, the path setupinitiator sends a working path setup message back to the source networkdevice over the first ringlet, as well as a protection path setupmessage to the same source device over the second ringlet. Each stationdevice further employs a bandwidth reservation unit, which reservesbandwidth on the second ringlet to establish a working path of thespecified logical network segment when a working path setup message isreceived from the first ringlet. It also reserves bandwidth on the firstringlet to establish a protection path of the specified network when aprotection path setup message is received from the second ringlet.

The above and other objects, features and advantages of the presentinvention will become apparent from the following description when takenin conjunction with the accompanying drawings which illustrate preferredembodiments of the present invention by way of example.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a conceptual view of a communications system according andembodiment of to the present invention.

FIG. 2 is an overall block diagram of a communications system.

FIG. 3 shows ATD frames spread information about bandwidth requirementsof VLAN1.

FIG. 4 shows a bandwidth table.

FIG. 5 shows how a working path and a protection path are determined.

FIG. 6 shows how working path setup messages and protection path setupmessages are delivered.

FIG. 7 shows a protection path setup message propagating toward astation.

FIGS. 8A and 8B show a bandwidth table and a link table.

FIG. 9 shows the reserved bandwidth of every link.

FIG. 10 provides an overview of an RPR network.

FIG. 11 shows RPR classes of service.

FIG. 12 shows a conventional way of reserving bandwidth.

FIG. 13 shows a problem of conventional bandwidth reservation.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Preferred embodiments of the present invention will be described belowwith reference to the accompanying drawings, wherein like referencenumerals refer to like elements throughout.

FIG. 1 is a conceptual view of a communications system according to anembodiment of the present invention. This communications system 1 isformed from a plurality of station devices (also referred to as “networkdevices”) 10-1 to 10-n (collectively referred to by the referencenumeral “10”). Those station devices 10 are interconnected by fiberoptic transmission media in a redundant ring topology to provide RPRcommunication service. The outer and inner rings are referred to asfirst and second ringlets R0 and R1. Each station device 10 has, amongothers, a bandwidth reservation initiator 11, a topology database 12, apath setup initiator 13, a bandwidth reservation unit 14, abandwidth/link manager 15, a traffic controller 16, and I/O interfaces(I/F) 17 a and 17 b.

The I/O interface 17 a shown on the left-hand side of FIG. 1 handlesincoming data traffic from the first ringlet as well as outgoing datatraffic to the second ringlet. The I/O interface 17 b on the other sidehandles incoming data traffic from the second ringlet and outgoing datatraffic to the first ringlet.

The bandwidth reservation initiator 11 sends out a bandwidth reservationmessage to both ringlets attached to the station device 10. Thisbandwidth reservation message contains a source identifier, a logicalnetwork identifier, and a bandwidth reservation value, so as to announcehow much bandwidth should be reserved for a network path. Specifically,the logical network identifier may be a VLAN identifier (VLAN ID) in thecase that the network path is of a VLAN domain. In the case of amulti-protocol label switching (MPLS) network, its MPLS label will beincluded as a logical network identifier. The following description willassume VLANs, and thus the bandwidth reservation messages are supposedto contain a VLAN identifier in their logical network identifier fields.

The topology database 12 manages hop counts measured from the presentstation device 10 to other station devices on the ring. The hop countrefers to the number of station-to-station links that have to betraversed to reach a remote station device. Since the number ofintervening links depends on which ring direction to follow, the hopcounts of a station device actually include a first hop count measuredalong the first ringlet and a second hop count measured along the secondringlet.

The path setup initiator 13 receives a bandwidth reservation messagefrom other station devices and examines its source identifier and VLANidentifier fields, thus determining whether the local station device 10is the egress node of the specified VLAN. If that is the case, then thepath setup initiator 13 consults the topology database 12 to retrievethe first and second hop counts measured from the destination stationdevice (i.e., the present station device 10 itself) to the sourcestation device along the first and second ringlets, respectively.Suppose now that the first hop count is smaller than the second hopcount. Then the path setup initiator 13 sends a working path setupmessage back to the source network device over the first ringlet, aswell as transmitting a protection path setup message to the same sourcenetwork device over the second ringlet.

The bandwidth reservation unit 14 establishes a requested path asspecified by a working path setup message or a protection path setupmessage. Specifically, when a working path setup message is receivedfrom the first ringlet, the bandwidth reservation unit 14 reservesbandwidth on the second ringlet to establish a working path of thespecified VLAN. When a protection path setup message is received fromthe second ringlet, the bandwidth reservation unit 14 reserves bandwidthon the first ringlet to establish a protection path for the specifiedVLAN. Note that, in both cases, a path is established in the oppositedirection to the message-carrying ringlet. That is, a path will beestablished on the first ringlet if the request message is received fromthe second ringlet, and on the second ringlet if the message is receivedfrom the first ringlet. The bandwidth reservation unit 14 reservesbandwidth for each path in this way.

The bandwidth/link manager 15 updates and manages information aboutreserved bandwidth of VLANs with each received bandwidth reservationmessage. As will be described later, the bandwidth/link manager 15maintains a bandwidth table for this purpose. The bandwidth/link manager15 also receives a working path setup message or a protection path setupmessage of a specific VLAN and uses them to update link parameters ofevery link constituting the ring network. The link parameters of a linkindicate whether that link serves as part of a working path or aprotection path of a VLAN. A link table is employed for this purpose, aswill be described later.

The amount of reserved bandwidth may differ from path to path. Also theamount of available best-effort traffic bandwidth may differ from linkto link. If both of the above are true, the traffic controller 16defines a best-effort traffic bandwidth by choosing a minimum availablebandwidth of all links. More details of traffic control will be providedlater.

Communications System

FIG. 2 is an overall block diagram of a communications system 1, inwhich the station devices 10-1 to 10-n of FIG. 1 are renamed as stationsS1 to Sn. Those stations S1 to S6 are interconnected in a dual ringtopology. The two rings are named Ringlet0 and Ringlet1. Data trafficflows counterclockwise on Ringlet0, and clockwise on Ringlet1. Eachringlet has a capacity of 100 Mbps.

Suppose now that VLAN1 needs a bandwidth of 50 Mbps, and that VLAN2needs a bandwidth of 100 Mbps. While FIG. 2 only shows their workingpaths, VLAN1 and VLAN2 also have their respective protection paths withthe same capacities on the other ring. The following explanation focuseson how to set up a VLAN1 path.

The working path of VLAN1 leaves the source station S3 and goes alongRinglet1 to the destination station S4. The protection path, on theother hand, is a roundabout path on Ringlet0, from the same sourcestation S3 to the same destination station S4. Similarly, the workingpath of VLAN2 leaves the source station S2 and goes along Ringlet1 tothe destination station S3. Its corresponding protection path runs alongRinglet0, from the same source station S2 to the same destinationstation S3.

The operator of this communications system 1 reserves a requiredbandwidth of a path by configuring the ingress station of that path.Specifically, the desired bandwidth of VLAN1 will be set in the stationS3, and that of VLAN2 will be set in the station S2. Now that thedesired bandwidth has been given to the source stations S3 and S2, theirrespective bandwidth reservation initiators 11 broadcast a bandwidthreservation message to their adjacent stations. Both ringlets are usedin this broadcast, and the transmitted message propagates to allstations. Each station forwards received bandwidth reservation messagesfrom east port to west port, as well as from west port to east port.

Bandwidth reservation messages are carried by packets called attributediscovery (ATD) frames. ATD frames have data fields carrying a sourceidentifier, reserved bandwidth, and VLAN ID. FIG. 3 shows how ATD framesspread information about bandwidth requirements of VLAN1. Note that thesource identifier field of ATD frames is not depicted in FIG. 3. Thesource station S3 broadcasts an ATD frame to both ringlets. Morespecifically, ATD frames f1 and f2 are sent out to Ringlet1 andRinglet0, respectively. Likewise, another source station S2 broadcasts aVLAN2 bandwidth reservation message in both directions in the same wayas in the case of VLAN1.

Bandwidth Table Configuration

When an ATD frame is received, the bandwidth/link manager 15 in thereceiving station updates its own bandwidth table with the values ofreserved bandwidth and VLAN ID. FIG. 4 shows the contents of a bandwidthtable T1 in a remote station S1, which has received ATD frames from itsneighboring stations. The illustrated bandwidth table T1 is actuallyformed from two subtables, one for Ringlet0 and the other for Ringlet0.Upon receipt of an ATD frame f1 through Ringlet0, the station S1extracts data fields describing VLAN ID=1 and its corresponding Class-A0bandwidth value of 50 Mbps. The station S1 then updates its localbandwidth table T1 by writing the extracted parameters into the Ringlet0subtable.

The station S1 also processes another ATD frame f2 received throughRinglet1 in a similar way. That is, the station S1 finds VLAN ID=1 andits Class A0 bandwidth value of 50 Mbps in the received frame f2. Thestation S1 then updates its bandwidth table T1 by writing the extractedparameters into the Ringlet1 subtable.

Path Usage Determination

FIG. 5 shows how a working path and a protection path are determined.When an ATD frame arrives at the egress station S4 of VLAN1, its localpath setup initiator 13 determines where to place a working path and aprotection path. The station S4 knows that the station S3 is the onlystation that is supposed to have a VLAN1 connection to the station S4itself. For this reason, the station S4 can immediately recognize itselfas being the egress node of VLAN1 from the fact that the received ATDframe f1 contains a source identifier of S3 and a VLAN ID of “VLAN1.”The source identifier tells the path setup initiator 13 which station isthe ingress node of VLAN1, which is S3 in the present example. The pathsetup initiator 13 then consults the topology database 12 to obtain thehop counts of the ingress station S3 measured along Ringlet0 andRinglet1.

The topology database 12 in a station stores hop count information foreach of Ringlet0 and Ringlet1, showing how many links have to betraversed to reach other stations. In the case of station S4, itstopology database 12 gives a hop count value of one in the entry ofRinglet0 and station S3, meaning that the station S3 is just one linkaway from the present station S4. The topology database 12 also containsa hop count value of five in the entry of Ringlet1 and station S3,meaning that five links have to be traversed to reach the station S3.

Since the hop count of Ringlet0 is smaller than that of Ringlet1, thepath setup initiator 13 in the egress station S4 places a working pathsetup message on Ringlet0 (also referred to as the “first ringlet”) sothat the ingress station S3 can receive them. The path setup initiator13 further places a protection path setup message on Ringlet1 (alsoreferred to as the “second ringlet”), so that the ingress station S3 canreceive them from the opposite direction.

FIG. 6 shows how a working path setup message and a protection pathsetup message are delivered. A working path setup message is sent fromthe egress station S4 to the ingress station S3 through Ringlet0 (firstringlet). A protection path setup message, on the other hand, travels along way along Ringlet1 (second ringlet) to reach the ingress stationS3.

FIG. 7 shows a protection path setup message propagating toward astation S1. The path setup initiator 13 in the source station S4 hassent this protection path setup message to carry the following dataitems: destination identifier, source identifier, ringlet identifier,and path usage parameter. The path usage parameter field specifieswhether to set up a working path or a protection path. It also indicateswhich VLAN the path should serve.

In the present example of FIG. 7, the destination and source identifierfields carry the values of “S3” and “S4,” respectively, since theprotection path setup message has been addressed from the source stationS4 to the destination station S3. Also, the ringlet identifier fieldcontains a value of “1” since the message has been placed on Ringlet1.The path usage parameter field specifies “protection” and “VLAN1,”meaning that the message is intended for establishing a VLAN1 protectionpath.

Note that the path usage specified in a message received through acertain ringlet is opposite to the actual usage of that ringlet. Forexample, if a protection path setup message is received from Ringlet1,it means that Ringlet1 will be used as a working path. Therefore, thebandwidth reservation unit 14 in the receiving station S1 interprets theprotection path setup message shown in FIG. 7 as specifying thatRinglet1 be used as a VLAN1 working path, and that the opposite ringlet,Ringlet0, be used as a VLAN1 protection path. The bandwidth reservationunit 14 in the station S1 then configures the opposite ringlet,Ringlet0, so that it will serve as part of the specified protectionpath.

It should also be noted that the working path setup message andprotection path setup message are both addressed from the egress stationto the ingress station. The source and destination of those messages areopposite to the source node and destination node of a new path to beestablished. Think of, for example, a protection path setup messagecarrying a destination identifier of S3 and a source identifier of S4.This means that a protection path is supposed be routed, not from S4 toS3, but from S3 to S4. Likewise, if a working path setup message carriesa destination identifier of S3 and a source identifier of S4, it meansthat a working path is supposed to be routed from S3 to S4.

After all, the protection path setup message shown in FIG. 7 informs thereceiving station S1 that a VLAN1 protection path will be routed from S3to S4 on Ringlet0. The bandwidth reservation unit 14 in the station S1consults its own topology database 12 to know how the stations arearranged in the present ring network. The bandwidth reservation unit 14is thus able to reserve bandwidth for the VLAN1 protection path. Morespecifically, it registers this protection path with a link table T2(described in the next section). In the example of FIG. 7, theprotection path has to have a capacity of 50 Mbps as previouslyannounced by ATD frame broadcasting. The bandwidth reservation unit 14can retrieve this bandwidth requirement by consulting its localbandwidth table T1.

Management of Bandwidth Table and Link Table

FIGS. 8A and 8B show the bandwidth table T1 and link table T2 managed bythe bandwidth/link manager 15 in the station S1. The illustrated linktable T2 has the following link parameter fields: “Link,” “VLAN(working),” “VLAN (protection),” and “Ringlet.” The link field containsa link identifier (see FIG. 7). The stations exchange link parameterscontained in their respective link tables T2 when any change is made tothe table entries, thereby keeping a common set of latest linkparameters in their respective link tables T2.

Specifically, the topmost entry k0 of the link table T2 shows that Link0of Ringlet0 serves as part of protection paths of VLAN1 and VLAN2.Another entry k1 indicates that Link2 of Ringlet1 is used as a VLAN2working path. Yet another entry k2 shows that Link3 of Ringlet0 servesas part of a VLAN2 protection path. Other entries can be interpreted ina similar way. As can be seen from this example, the link table T2 andbandwidth table T1 permit each station to manage the Class A0 bandwidthfor each link and each path (or each VLAN).

It may be noticed that the Ringlet0 subtable of the bandwidth table T1has been emptied. This means that the station S1 has updated itsbandwidth table T1 to reflect the fact that the reserved 50 Mbps and 100Mbps are assigned to the protection paths of VLAN1 and VLAN2,respectively. The bandwidth table T1 only maintains entries of theRinglet1 subtable representing reserved bandwidth of each VLAN's workingpath.

FIG. 9 shows the reserved bandwidth of every link. As can be seen fromthe bandwidth table T1 of FIG. 8A and the link table T2 of FIG. 8B, theVLAN2 working path runs on Link2 of Ringlet1, and 100 Mbps is thusreserved for that Link2. The VLAN1 working path, on the other hand, runson Link3 of Ringlet1, and 50 Mbps is thus assigned to that Link3.

Link0 of Ringlet0 is used by both VLAN1 and VLAN2 to provide theirprotection paths. VLAN1 would be switched to its protection path in theevent of failure in Link3 of Ringlet1. Likewise, VLAN2 would be switchedto its protection path in the event of failure in Link2 of Ringlet1. Theprotection path of VLAN2 overlaps with that of VLAN1, and VLAN2 takes upa greater bandwidth (100 Mbps) than VLAN1. In such a case, reserving 100Mbps on Ringlet0 would suffice for all VLAN paths. Details will bediscussed in the next section.

Bandwidth Reservation for Protection Paths

Bandwidth of working paths should be fully reserved in all linksconstituting them. In the present example, both VLAN1 working path (S3to S4) and VLAN2 working path (S2 to S3) are allocated independentbandwidth resources. The present embodiment, however, takes a differentapproach for protection paths. Specifically, the present embodimentdetermines the total amount of bandwidth reservation for protectionpaths by taking potential failure points of each VLAN intoconsideration. The term “potential failure point” refers to a point onthe network at which a link failure would cause a failover of VLAN.

More specifically, it appears, in the above example, to be necessary toreserve 150 Mbps on Link0 of Ringlet0 since Link0 must provide bandwidthto both VLAN1 and VLAN2 protection paths. It should be noticed, however,that the potential failure point of VLAN1 is Link3, whereas that ofVLAN2 is Link2. Failure of VLAN1 does not affect VLAN2, and vice versa.This fact suggests that there is no need for VLAN1 and VLAN2 to keepfull spare bandwidth since it is quite unlikely that both VLANs fail atthe same time. Because the bandwidth requirement of VLAN2 is larger thanthat of VLAN1 in the present example (100 Mbps>50 Mbps), a 100-Mbpsreservation of VLAN2 could also be used to back up VLAN1 in the event offailure. Conventional systems, however, simply reserve every provisionedbandwidth along both ringlets, thus failing to make efficient use ofbandwidth resources.

According to the present embodiment, the amount of protection bandwidthreservation is calculated on an individual link basis. Although two ormore protection paths may share a single link, it does not always meanthat the link is required to provide all those protection pathsconcurrently. Rather, the concurrence of protection paths depends onwhether they share a potential failure point. In the example shown inFIGS. 8 and 9, a failure in Link2 would not cause failover of VLAN1.Rather, Link0 is only required to back up VLAN2 in that event.Therefore, the present embodiment first enumerates every possibleconcurrent protection path running on a link, taking into considerationall potential failure points of VLAN paths. The present embodiment thenselects, from among the enumerated paths, a widest protection path onthat link and reserves as much bandwidth as the selected protection pathrequires.

As can be seen from the above explanation, the communications system 1of the present embodiment is designed to reserve Class-A0 bandwidth onan individual path (or individual VLAN) basis. Conventionalcommunications systems consume excessive bandwidth in an attempt toreserve all required Class-A0 bandwidth regardless of their actualroutes, thus hampering addition of new paths or causing other problems.Unlike such conventional systems, the proposed communications system 1eliminates the need for superfluous bandwidth reservation because of itsadvantageous features of path-based reservation and link management. Thebandwidth resources can be used more efficiently since thecommunications system 1 reserves bandwidth of protection paths by takinginto consideration which paths would be switched in the event of linkfailure. The present invention therefore contributes to an improvedoperability of an RPR network.

Best-Effort Traffic Control

The present embodiment provides a traffic controller 16 to supportbest-effort traffic control. Since best-effort traffic is called“fairness eligible traffic” in the RPR terminology, the latter term willbe used in the following section.

The communications system 1 transports fairness eligible traffic usingnon-reserved bandwidth resources of the network. Referring back to FIG.9, suppose that each ringlet has a capacity of 150 Mbps. VLAN1 takes up50 Mbps out of the Ringlet1 capacity for its working path (S3 to S4,clockwise), besides reserving 50 Mbps out of the Ringlet0 capacity forits protection path (S3 to S4, counterclockwise). The bandwidthremaining on Link2 of Ringlet0 is therefore 100 Mbps, which is availablefor fairness eligible traffic.

Also, VLAN2 takes up 100 Mbps out of the Ringlet1 capacity for itsworking path (S2 to S3, clockwise), besides reserving 100 Mbps out ofthe Ringlet0 capacity for its protection path (S2 to S3,counterclockwise). The bandwidth remaining on Link1 of Ringlet0 is 50Mbps, which is available for fairness eligible traffic.

Suppose now that station S3 needs to send station S2 a certain amount offairness eligible packets. The sending station S3 can send out thistraffic at 100 Mbps since Link2 of Ringlet0 allows it. However, the nexthop, (i.e., Link1) only provides a capacity of 50 Mbps for fairnesseligible traffic. Because of this bottle neck, one half of thetransmitted packets are discarded at the next station S2, the lostpackets being equivalent to 50 Mbps.

As the above example shows, different fairness eligible capacities ofadjacent links would lead to a packet loss problem. To address theproblem, the present embodiment places an upper limit to fairnesseligible traffic on each ringlet. In short, the upper limit will bedetermined as a minimum available bandwidth of all links.

Fairness eligible traffic is only allowed to use a fraction of thecapacity of each link, the amount of which is calculated by subtractingexisting Class-A0 bandwidth from the original ring capacity. The morethe Class-A0 traffic reserves, the less the fairness eligible trafficcan use. The traffic controller 16 therefore scans the bandwidth tableT1 and link table T2 to find a maximum reservation of Class A0bandwidth. This maximum bandwidth reservation is then used to determinean upper limit of fairness eligible traffic.

Referring again to FIGS. 8A and 8B, VLAN2 reserves 100 Mbps for use asits working path, which is the largest consumer of the Ringlet1bandwidth. The largest consumption on Ringlet0 is also 100 Mbps, whichis reserved by VLAN2 for use as a protection path. Since the originalnetwork capacity is 150 Mbps per ringlet, the traffic controller 16determines that the fairness eligible traffic must be limited to 50Mbps. This upper limit applies to all links on both Ringlet0 andRinglet1.

As can be seen from the above discussion, the traffic controller 16 isdesigned to determine a minimum bandwidth available for fairnesseligible traffic. This is achieved by scanning all links to find amaximum reserved bandwidth and subtracting that maximum reservedbandwidth from the original ring capacity. This feature of the trafficcontroller 16 prevents fairness eligible packets from being lost in themiddle of their travel over ringlets, even in the case where theremaining bandwidth differs from link to link because of the unevennessof path bandwidth reservations.

Advantages

As can be seen from the preceding discussion, the present inventionoffers the following advantages:

-   -   Class-A0 bandwidth can be reserved on an individual path basis,        thus enabling efficient use of bandwidth resources.    -   Information on Class-A0 bandwidth can be managed and reported on        an individual path basis.    -   Bandwidth reservation applies, not only to working paths, but        also to protection paths for improved availability.    -   A database is provided to manage the information about which        links constitute each working and protection path. This database        allows every station to see which stations each path traverses.    -   Packet loss is minimized in transport of fairness eligible        traffic.

CONCLUSION

According to the communications system of the present invention, theegress station of a network path will determine which ringlet to use toset up a working path, by comparing hop counts of the ingress stationmeasured in different ring directions. The egress station sends aworking path setup message to a first ringlet with a smaller hop count,and a working path setup message to a second ringlet with a larger hopcount. Those messages are addressed to the ingress station. When aworking path setup message is received from the first ringlet, thereceiving station reserves bandwidth on the second ringlet to establisha working path of the specified logical network segment. When aprotection path setup message is received from the second ringlet, thereceiving station reserves bandwidth on the first ringlet to establish aprotection path of the specified network. The proposed mechanism permitsefficient use of bandwidth resources by reserving them on an individualpath basis, besides improving operability of ring networks.

The foregoing is considered as illustrative only of the principles ofthe present invention. Further, since numerous modifications and changeswill readily occur to those skilled in the art, it is not desired tolimit the invention to the exact construction and applications shown anddescribed, and accordingly, all suitable modifications and equivalentsmay be regarded as falling within the scope of the invention in theappended claims and their equivalents.

1. A communications system transporting data over a redundant ringnetwork formed from first and second ringlets running in oppositedirections, the system comprising: (a) a plurality of station devices,each comprising: a bandwidth reservation initiator that sends out abandwidth reservation message in both ring directions to announce howmuch bandwidth should be reserved for a network path, the bandwidthreservation message containing a source identifier, a logical networkidentifier, and a bandwidth reservation value, a topology database thatmanages hop counts of other station devices on the ring network, the hopcounts including first hop counts measured along the first ringlet andsecond hop counts measured along the second ringlet, a path setupinitiator that examines a source identifier and logical networkidentifier in a bandwidth reservation message received from otherstation devices, thereby recognizes that the local station device is anegress node of a logical network segment specified in the receivedbandwidth reservation message, consults the topology database toretrieve the first and second hop counts of the source station device ofthe received bandwidth reservation message, and, if the retrieved firsthop count is smaller than the retrieved second hop count, sends aworking path setup message back to the source network device over thefirst ringlet, as well as transmitting a protection path setup messageto the same source device over the second ringlet, and a bandwidthreservation unit that reserves bandwidth on the second ringlet toestablish a working path of the specified logical network segment when aworking path setup message is received from the first ringlet, andreserves bandwidth on the first ringlet to establish a protection pathof the specified network when a protection path setup message isreceived from the second ringlet; and (b) a plurality of transmissionmedia interconnecting the station devices to form the first and secondringlets.
 2. The communications system according to claim 1, wherein:the station device further comprises a bandwidth/link manager comprisinga bandwidth table and a link table; the bandwidth/link manager updatesthe bandwidth table with each received bandwidth reservation message tomaintain latest information about reserved bandwidth of each logicalnetwork segment; and the bandwidth/link manager updates the link tablewith each received working path setup message and protection path setupmessage to maintain link parameters for each link of the first andsecond ringlets, wherein the link parameter of a link indicates whetherthat link is used as part of a working path or as part of a protectionpath of a particular logical network segment.
 3. The communicationssystem according to claim 1, wherein the working path setup message andprotection path setup message produced by the path setup initiatorinclude at least one of: a destination identifier, a source identifier,a ringlet identifier, and a path usage parameter specifying whichlogical network segment to establish, as well as indicating whether thespecified path is used as a working path or as a protection path of thatlogical network segment.
 4. The communications system according to claim3, wherein: the bandwidth reservation unit establishes a path with aslarge bandwidth as specified by the bandwidth reservation value in thepreviously received bandwidth reservation message; the established pathserves as a working path or protection path as specified by the receivedpath usage parameter; the established path is oriented in an oppositedirection to what the received destination and source identifierssuggest; and the established path runs on an opposite ringlet to whatthe received ringlet identifier suggests.
 5. The communications systemaccording to claim 1, wherein the station device further comprises atraffic controller that defines a best-effort traffic bandwidth bychoosing a minimum available bandwidth of all links in the case wherethe amount of reserved bandwidth differs from path to path and where theamount of available best-effort traffic bandwidth differs from link tolink.
 6. The communications system according to claim 1, wherein thebandwidth reservation unit determines the amount of bandwidth for theprotection path by calculating a maximum amount of total reservedbandwidth that must be switched at the same time in the event offailure.
 7. A network device for use in a redundant ring network formedfrom first and second ringlets running in opposite directions, thedevice comprising: a bandwidth reservation initiator that sends out abandwidth reservation message in both ring directions to announce howmuch bandwidth should be reserved for a network path, the bandwidthreservation message containing a source identifier, a logical networkidentifier, and a bandwidth reservation value; a topology database thatmanages hop counts of other station devices on the ring network, the hopcounts including first hop counts measured along the first ringlet andsecond hop counts measured along the second ringlet; a path setupinitiator that examines a source identifier and logical networkidentifier in a bandwidth reservation message received from otherstation devices, thereby recognizes that the local station device is anegress node of a logical network segment specified in the receivedbandwidth reservation message, consults the topology database toretrieve the first and second hop counts of the source station device ofthe received bandwidth reservation message, and, if the retrieved firsthop count is smaller than the retrieved second hop count, sends aworking path setup message back to the source network device over thefirst ringlet, as well as transmitting a protection path setup messageto the same source device over the second ringlet; and a bandwidthreservation unit that reserves bandwidth on the second ringlet toestablish a working path of the specified logical network segment when aworking path setup message is received from the first ringlet, andreserves bandwidth on the first ringlet to establish a protection pathof the specified network when a protection path setup message isreceived from the second ringlet.
 8. A method of transporting data usingbandwidth reserved on a redundant ring network formed from first andsecond ringlets running in opposite directions, the method comprisingthe steps of: (a) broadcasting a bandwidth reservation message in bothring directions to announce how much bandwidth should be reserved for anetwork path, the bandwidth reservation message containing a sourceidentifier, a logical network identifier, and a bandwidth reservationvalue; (b) providing a topology database to manage hop counts of otherstation devices on the ring network, the hop counts including first hopcounts measured along the first ringlet and second hop counts measuredalong the second ringlet; (c) examining a source identifier and logicalnetwork identifier in a received bandwidth reservation message, therebyrecognizing that the local station device is an egress node of a logicalnetwork segment specified in the received bandwidth reservation message;(d) consulting the topology database to retrieve the first and secondhop counts of the source station device of the received bandwidthreservation message; (e) sending a working path setup message back tothe source network device over the first ringlet, as well as aprotection path setup message to the same source device over the secondringlet, if the retrieved first hop count is smaller than the retrievedsecond hop count; (f) reserving bandwidth on the second ringlet toestablish a working path of the specified logical network segment when aworking path setup message is received from the first ringlet; and (g)reserving bandwidth on the first ringlet to establish a protection pathof the specified network when a protection path setup message isreceived from the second ringlet.
 9. The method according to claim 8,further comprising the steps of: updating a bandwidth table with eachreceived bandwidth reservation message to maintain latest informationabout reserved bandwidth of each logical network segment; and updating alink table with each received working path setup message and protectionpath setup message to maintain link parameters for each link of thefirst and second ringlets, wherein the link parameter of a linkindicates whether that link is used as part of a working path or as partof a protection path of a particular logical network segment.
 10. Themethod according to claim 8, wherein the working path setup message andprotection path setup message sent in said sending step (e) include atleast one of: a destination identifier, a source identifier, a ringletidentifier, and a path usage parameter specifying whether to set up aworking path or a protection path, as well as indicating which logicalnetwork segment the path should serve.
 11. The method according to claim10, further comprising establishing a path with as large bandwidth asspecified by the bandwidth reservation value in the previously receivedbandwidth reservation message, upon receipt of the working path setupmessage or the protection path setup message; the established pathserves as a working path or protection path as specified by the receivedpath usage parameter; the established path is oriented in an oppositedirection to what the received destination and source identifierssuggest; and the established path runs on an opposite ringlet to whatthe received ringlet identifier suggests.
 12. The method according toclaim 8, further comprising the step of defining a best-effort trafficbandwidth by choosing a minimum available bandwidth of all links in thecase where the amount of reserved bandwidth differs from path to pathand where the amount of available best-effort traffic bandwidth differsfrom link to link.
 13. The method according to claim 9, furthercomprising the step of determining the amount of bandwidth for theprotection path by calculating a maximum amount of total reservedbandwidth that must be switched at the same time in the event offailure.